Acid herbicides such as 2,4-dichlorophenoxyacetic acid (2,4-D) have long been used to control unwanted vegetation. 2,4-D is normally converted into liquid formulations by conversion to water soluble salts or emulsified esters. The ester formulations have been found to be more effective than the salts on an acid equivalent basis in the control of noxious vegetation but have the unwanted characteristic of migrating to adjacent desirable vegetation because of the volatility thereof, resulting in unacceptable damage to sensitive plants.
Efforts to solve the volatility problem, including preparation of water soluble salts such as the dimethylamine salt of 2,4-D, have not been totally satisfactory because, upon volatilization of the amine, the herbicide reverts back to its initial acid form, which, in itself under certain unfavorable conditions, has sufficient volatility to cause damage to sensitive crops.
2,4-D ester or 2,4-D dimethylamine formulations applied during the warm summer months can lead to vapor drift from the evaporation of the herbicide from sprayed surfaces and subsequent damage to highly susceptible crops such as tomatoes, cotton, soybeans, sunflowers and grapes. This may occur within hours after the herbicide application.
Thus it would be desirable to have an herbicidal carboxylic acid derivative that is at least as active as the commercially used carboxylic acid herbicide salts, but which is less volatile so that its use would not damage nearby sensitive crops.